1. Field of the Invention
This invention relates to a liquid injection recording head and a liquid injection recording apparatus provided with the head, and in particular to a liquid injection recording head of the full multitype in which recording elements used to discharge recording liquid from a discharge opening and accomplish recording by flying liquid droplets are arranged by a number corresponding to the recording width, and a liquid injection recording apparatus provided with such head.
2. Description of the Related Background Art
As for liquid injection recording heads of this type, there have heretofore been proposed various heads such as a head in which a pressure charge is produced in the liquid in a liquid path by deformation of a piezoelectric element to thereby discharge minute liquid droplets, a head in which a pair of electrodes are provided near a discharge opening to thereby deflect liquid droplets and accomplish recording, and a head in which a heat generating element disposed in a liquid path is suddenly caused to generate heat to thereby produce bubbles in the liquid and the bubbles are utilized to discharge the liquid as liquid droplets from a discharge opening.
Among these, the last-mentioned system utilizing heat energy can be said to be particularly effective liquid injection recording head because of its feature that highly dense arrangement of discharge openings is easy and high-speed recording is possible. Also, as such a recording head, there are known as the serial scan type and the full multi (full line) type in which recording elements are arranged corresponding to the recording width, but from the viewpoint of high-speed recording, the full multitype is apparently more advantageous.
FIG. 1 of the accompanying drawing shows an example of the construction of a liquid injection recording head of such full multitype and the ink supply means thereof. In FIG. 1, the reference numeral 1 designates the recording head, the reference numeral 2 denotes a common liquid chamber in the recording head 1, and the reference numeral 3 designates discharge openings for liquid discharge arranged in a recording liquid discharge opening surface 4. The discharge openings 3 in the present example are arranged over the full recordable width of a recording material to be recorded and heat generating elements which are energy generating means provided in a liquid path, not shown, leading to the individual discharge openings 3 are selectively driven to thereby discharge the recording liquid, whereby recording can be accomplished without the main scanning of the head the heat itself. In the heat generating elements, use is made, for example, of electro-thermal converting members each having a heat generating resistance layer and an electrode connected to the heat generating resistance layer.
The reference numeral 5 designates a recording liquid supply tank for supplying the recording liquid to the recording head 1, and the reference numeral 6 denotes a main tank for replenishing the supply tank 5 with the recording liquid. The recording liquid is supplied from the supply tank 5 to the common liquid chamber 2 of the recording head 1 by a supply tube 7, and during the replenishment with the recording liquid, the recording liquid can be supplied from the main tank 6 to the supply tank 5 by a pump 9 for recovery through a one-way rectifying valve 8 for replenishment. The reference numeral 10 designates a one-way rectifying valve for recovery during the recovering operation effected to recover the discharging function of the recording head 1, the reference numeral 11 denotes a circulation tube in which the rectifying valve 10 for recovery is disposed, the reference numeral 12 designates an electromagnetic valve disposed in the aforementioned first supply tube 7, and the reference numeral 13 denotes a vent valve for the supply tank.
In the recording head 1 thus constructed, and the recording liquid supply system and recovering system thereof, the electromagnetic valve 12 is kept open during recording, and the recording liquid is supplied from the gravity or the like thereof from the supply tank 5 to the common liquid chamber 2 and is directed from the liquid chamber 2 to the discharge openings 3 through a liquid path, not shown. Also, during the recovering operation carried out to remove bubbles remaining in the common liquid chamber 2 and the supply system and cool the recording head 1, the pump 9 for recovery is driven to supply the recording liquid into the common liquid chamber 2 by the circulation tube 11, and the recording liquid can be returned from the common liquid chamber 2 to the supply tank 5 by the first supply tube 7. Further, during the initial filling of the liquid path or the like with the recording liquid, the recording liquid can be forced into the common liquid chamber 2 via the circulation tube 11, which is the second supply tube, by the pump 9 with the electromagnetic valve 12 closed, whereby bubbles can be discharged and the recording liquid can be discharged from the discharge openings 3.
However, in the conventional multi-nozzle type liquid injection recording head, as described above, when high-density recording such as solid recording by the head generating elements, particularly, high-speed recording by the high-frequency driving of the heat generating elements, is carried out, any excess heat not used for recording (to form liquid droplets) and heat generated from a driver for driving the heat generating elements accumulate during long-time recording and, moreover, a temperature gradient by such heat distribution may sometimes occur to the recording liquid in the common liquid chamber.
Describing such a phenomenon with reference to FIGS. 2A-2C of the accompanying drawings, in the case of a recording head as shown in FIG. 2B, the temperature of the recording liquid inevitably becomes high near the central portion of the recording head and the the temperature of the recording liquid supplied is low because it accommodates itself to the environmental temperature. So, the recording liquid in the common liquid chamber assumes the temperature gradient as shown in FIG. 2C and as a result, a difference occurs in the viscosity of the recording liquid, and liquid droplets discharged from the right discharge opening which is at a high temperature become greater in viscosity than liquid droplets discharged from the left discharge opening, whereby on a recording medium 30 shown in FIG. 2A, the record on the right half becomes dense or dark as compared with the record on the left half and thus, the quality of recording is spoiled. Such a tendency becomes more remarkable as the number of discharge openings becomes greater, e.g. 128 or 256, and some countermeasure has been desired.